AVR-Chat

Thanks, that answers my questions.  I guess I need to RTM.  :)

It appears as though I'd need the external crystal for temperature
stability and no processor overhead (vs real time corrections in the
datasheet)

Is there any instance where ISP will fail?  


--- In AVR-Chat@yahoogroups.com, Ned Konz <ned@...> wrote:
>
> Ryan wrote:
> 
> > I'm going to take the step away from DIP, to TQFP!  WOOO!!!  My next
> > design is going to use the Mega16 in the 44pin TQFP package. 
> > Obviously I can't use my STK500 to program it anymore.
> 
> Why is that? You can run the ISP connections from the STK500 to your 
> target board. This is documented in the STK500 manual.
> 
> > So - what do you use?
> 
> STK500
> AVR-JTAG mkI clone by Olimex
> AVR-JTAG mkII by Atmel
> AVRISP mkI by Atmel
> 
> > 
> > I've heard people mention a "JTAG"?  Does that allow complete
> > programming?  Fuses and eeprom too?  Any special tips I need to know?
> 
> They support all the programming (see your datasheet for details, 
> though). The JTAG units also allow debugging, typically.
> 
> > My second question, is how reliable is the internal RC clock?  It's
> > tough for me to trust them, so I have been using an external
> > crystal... but... in the interest of real estate, costs, and ease of
> > assembly, I'm considering switching to the internal clock.  However -
> > one thing I'm concerned about is the RS232 interface.  If the internal
> > clock is 7.9mhz instead of the desired 8mhz, will that make a
> > difference?  How are tolerances?
> 
> The RC oscillators can be trimmed to get them reasonably close.
Refer to 
> your datasheet for details (in the section called "calibrated internal 
> RC oscillator").
> 
> You generally want the RS-232 to be within 2% or so (the tolerance is 
> dependent on how the receiver samples the signal).
> 
> There are details on calibration schemes in the datasheet as well as:
> http://atmel.com/dyn/resources/prod_documents/doc2555.pdf
> http://atmel.com/dyn/resources/prod_documents/doc2563.pdf
> http://atmel.com/dyn/resources/prod_documents/doc8002.pdf
> 
> -- 
> Ned Konz
> ned@...
> http://bike-nomad.com
>